Chapter 13 Quiz

Part A: Multiple Choice

1. In a main electrical panel, what component connects the two hot legs from the utility to the branch circuit breakers?

a) Neutral bus bars b) Grounding electrode conductors c) Hot busbars d) Main lugs

2. A circuit breaker trips instantaneously when you plug in an extension cord that has a direct short. Which mechanism in the breaker causes this fast trip?

a) The bimetallic thermal strip detecting heat from sustained overcurrent b) The electromagnetic solenoid responding to a massive instantaneous current surge c) The AFCI electronics detecting an arc fault signature d) The GFCI sensor detecting a ground fault imbalance

3. You have an old home with a Federal Pacific Stab-Lok panel. The most important reason to have this panel inspected and likely replaced is:

a) Federal Pacific went out of business and replacement breakers aren't available b) The panel can't accommodate AFCI breakers c) The breakers may fail to trip on overcurrent, eliminating circuit protection d) The panel is too old to be insured under any homeowners policy

4. You reset a tripped breaker with no devices plugged in, and it trips again immediately. This most likely indicates:

a) The breaker is old and needs to be recalibrated b) Too many circuits on the panel and the load needs to be redistributed c) A short circuit or ground fault in the wiring of that circuit d) The main breaker is overloaded

5. A 20-amp circuit should not be loaded above how many amps for continuous loads, according to the 80% rule?

a) 20 amps b) 15 amps c) 16 amps d) 18 amps

6. In a sub-panel (secondary panel in a detached garage), which of the following is the correct wiring practice?

a) The neutral bus and ground bus should be bonded together, exactly as in a main panel b) The neutral bus and ground bus must be kept separate; ground runs back to the main panel c) The neutral wire from the feeder can be omitted if all loads are 240V d) A sub-panel does not require a separate grounding electrode

7. A home has a 1,800 sq ft living area, an electric range (8,000 VA), an electric dryer (5,000 VA), an electric water heater (4,500 VA), a 3-ton heat pump (4,320 VA), and basic lighting/appliance loads. Using the simplified load calculation, approximately how many amps of calculated load does this home have?

a) About 80 amps b) About 120 amps c) About 150 amps d) About 200 amps

8. What distinguishes a tandem breaker from a standard single-pole breaker?

a) A tandem breaker provides protection for two separate circuits in one panel slot space b) A tandem breaker is rated for 240V circuits requiring two legs c) A tandem breaker has AFCI protection built in d) A tandem breaker is used as a main disconnect in sub-panels

9. You receive quotes for a 100-amp to 200-amp service upgrade from three licensed electricians. The lowest quote is $900 and the others are around $3,000. What is the most important question to ask the low bidder?

a) Whether they will use copper or aluminum service entrance conductors b) Whether the price includes the permit, utility coordination, and all required code upgrades c) Whether their work comes with a 5-year warranty d) Whether they can start immediately

10. You are adding circuits to your home for a kitchen renovation. Under current NEC, the new kitchen countertop circuits should have:

a) Standard single-pole breakers only — AFCI and GFCI protection is only required in bathrooms b) GFCI protection at outlets, AFCI protection at breakers (or combination protection) c) AFCI protection only; GFCI protection is not required in kitchens d) No special protection requirements since the NEC exempts appliance circuits

Part B: Short Answer

11. Isabel Rodriguez's 1982 townhouse has a 100-amp service. She wants to add an EV charger (48-amp Level 2) and upgrade from gas heat to a heat pump (18A at 240V). Her existing calculated load is approximately 68 amps. Walk through the decision about whether her service is adequate, using the concepts from Section 13.6.

12. Explain why it's dangerous to install a 20-amp breaker on a circuit wired with 14-gauge wire, even though the breaker is a larger, "stronger" protection device.

13. What is double-tapping in an electrical panel, why is it generally not acceptable, and what are the two correct solutions if a panel is full?

14. Describe three visible warning signs you might observe while mapping your panel (cover on, door open) that would indicate the panel needs professional attention. For each, explain what the sign indicates.

15. A homeowner has a 60-amp fuse box with original knob-and-tube wiring. They call you for advice about whether they need to upgrade. Give them a direct, honest assessment of the risks and the likely path forward, including realistic cost expectations.

Answer Key

Part A

  1. c) Hot busbars — The busbars are the metal conductor bars that distribute current from the service entrance to the branch circuit breakers; the main lugs are connection points for incoming service conductors, but the busbars are what feeds the breakers

  2. b) The electromagnetic solenoid — A short circuit causes a massive instantaneous current surge that creates a strong magnetic field, tripping the breaker mechanically in milliseconds. The thermal bimetallic strip is too slow for short circuit protection

  3. c) The breakers may fail to trip on overcurrent — This is the documented safety concern with Stab-Lok panels: the breakers can fail to open under overload or short circuit conditions, allowing circuits to overheat

  4. c) A short circuit or ground fault in the wiring — A breaker that trips immediately on reset with no load connected indicates a fault in the circuit wiring itself, not a load issue

  5. c) 16 amps — The NEC 80% continuous load rule: 20A × 80% = 16 amps for continuous loads (operating 3 hours or more)

  6. b) Neutral and ground must be kept separate in a sub-panel — The bonding jumper belongs only in the main panel (one bonding point per system). In sub-panels, neutral and ground are kept separate to prevent neutral current from flowing on ground conductors

  7. c) About 150 amps — Using the simplified method: lighting load ~5,940 VA, range 8,000 VA, dryer 5,000 VA, water heater 4,500 VA, heat pump 4,320 VA, dishwasher/other ~3,000 VA = approximately 30,760 VA ÷ 240V ≈ 128 amps; with a Level 2 EV charger it would exceed 150 amps. Without EV charging, approximately 120–130 amps depending on exact inputs.

  8. a) A tandem breaker provides protection for two circuits in one slot space — Tandem (or "duplex") breakers have two separate breaker mechanisms in the space of a single slot, allowing an additional circuit to be added to a full panel. They are not appropriate in all locations in all panels.

  9. b) Whether the permit, utility coordination, and code upgrades are included — A $900 quote for a service upgrade almost certainly excludes the permit, utility work, and code-required AFCI upgrades. Getting specifics on inclusions is essential before comparing quotes.

  10. b) GFCI protection at outlets, AFCI protection at breakers — Kitchen circuits require GFCI at outlets within 6 feet of sinks; new circuit wiring requires AFCI at the breaker per current NEC. Combination AFCI/GFCI outlets can satisfy both requirements at the device level.

Part B (Model Answers)

11. Current load: 68 amps. Adding the heat pump: 68 + 18 = 86 amps. Adding the EV charger (48A): 86 + 48 = 134 amps. Isabel's 100-amp service has a maximum of 100 amps — already exceeded at 134 amps. Even without the EV charger, 86 amps is 86% of the 100A service, exceeding the 80% guideline for comfort and headroom. The service upgrade to 200 amps is clearly necessary before either addition. At 200 amps, the calculated load of 134 amps represents 67% of service capacity — providing comfortable headroom of 33% (66 amps) for future additions.

12. A circuit breaker protects the wire, not the devices. The bimetallic strip in a 20-amp breaker is calibrated to trip at currents around and above 20 amps. But 14-gauge wire has an ampacity of only 15 amps — it can overheat and begin degrading its insulation at currents above that. With a 20-amp breaker, the circuit can carry 20 amps continuously without the breaker tripping, while the wire is experiencing overheating inside the wall. You can't see this happening. The wire's insulation degrades, eventually the bare conductors can contact nearby wood or insulation, and a fire begins inside the wall — long before the 20-amp breaker "protects" anything. The breaker must be sized for the wire, not the desired load.

13. Double-tapping occurs when two wires are connected under a single breaker terminal — a terminal designed for one wire. The connections are unreliable (one wire may not make full contact), and the circuit protection for each wire may be inadequate. It's also a code violation except in specific breakers rated for two conductors (which are clearly labeled as such). The two correct solutions for a full panel are: (1) Replace some standard breakers with tandem (duplex) breakers in spaces where the panel listing allows — this provides two circuit slots in one physical slot space; (2) Install a sub-panel to handle overflow circuits — appropriate when significant expansion is needed.

14. Three visible warning signs and their implications: - Scorching or discoloration visible around breakers or bus connections: Indicates overheating — an arc, a loose connection, or sustained overcurrent. The overheating may have damaged insulation or conductors. Requires electrician inspection with panel cover removed. - Two wires under one breaker terminal (double-tapping): Indicates the panel was filled and someone added circuits improperly. Both wire connections may be unreliable; circuit protection for the added circuit may be wrong for the wire gauge. Requires correction. - Breakers of different brands/manufacturers mixed in the panel: Most panels are listed for use with specific breaker brands. Mixing brands can void the panel listing and may result in breakers that don't properly fit the busbar — creating poor contact, heating, or failure to trip. Requires electrician assessment.

15. Direct assessment: A 60-amp fuse box with original knob-and-tube wiring is a combination of concerns that most electrical professionals and insurance companies will not regard as acceptable by modern standards. The 60-amp service is inadequate for virtually any modern home's electrical loads — it can't support central AC, electric appliances, or any significant modern demand. Knob-and-tube wiring has no equipment ground (meaning all your outlets are two-prong and equipment grounding is absent), and after 70+ years, the rubber insulation may be brittle and cracked, particularly in areas where it was covered by insulation in attic spaces. Most homeowners insurance carriers will either refuse to insure this configuration or charge significantly elevated premiums. The path forward is a full service upgrade to 200 amps and, depending on the condition and extent of the K&T, either a full rewire or a selective rewire of the affected circuits. Costs: service upgrade $2,500–$5,000; full house rewire $8,000–$20,000 depending on house size and conditions. A partial rewire of the most critical areas (kitchen, bathrooms, attic) is sometimes an interim step. This is a significant project — but the cost of a house fire exceeds it by orders of magnitude.